In order to convey a material to be conveyed such as a steel plate, paper, and a film, a conventional motor control apparatus drives, by means of motors, a plurality of conveyor rolls which are continuously arranged. The conventional motor control apparatus includes a speed control means. The speed control device receives, as an input, a deviation between a command speed and a motor speed, performs proportional-integral calculation to calculate a compensation torque so that the command speed and the motor speed coincide with each other, and outputs a command torque to the motor. The conventional motor control apparatus employs, in order to impart a tension to a material to be conveyed, draw control for generating a command value so that a speed difference (draw) is provided with respect to a predetermined base speed (or a predetermined reference speed). Moreover, the conventional motor control apparatus includes tension calculation means in order to control, by a simple adjustment, a tension of a material to be conveyed to coincide with a desired tension value. The tension calculation means calculates the tension of the material to be conveyed based on an acceleration/deceleration torque required by a motor for acceleration/deceleration, a mechanical torque, and a detected motor current. A draw setting for setting the speed difference is provided so that the calculated tension calculation value reaches a desired tension. After the speed difference is set so that the tension calculation value coincides with the desired tension, the tension calculation value on this occasion is held as a tension reference value. Moreover, the conventional motor control apparatus provides control, by activating tension control means for correcting the command speed, based on the tension reference value and the tension calculation value so that the tension of the material to be conveyed is maintained constant (refer to Patent Literature 1).
Moreover, another conventional motor control apparatus includes speed control means for calculating a compensation torque and adding the compensation torque to a torque command for driving a motor. The speed control means receives, as an input, a deviation between a command speed and a motor speed, and calculates a compensation torque so that the speed command and the motor speed coincide with each other by performing calculation for proportional control or proportional-integral control. Moreover, drooping control is used in order to avoid steady generation of an excessive torque, by an action of the speed control means. The drooping control is control for providing a drooping characteristic with which the motor speed decreases as the motor torque increases. In the drooping control, a speed droop amount, which is a proportional multiple of the compensation torque, is subtracted from the command speed. By the drooping control, even if there is a minute error between the command speed and a conveying speed at which a material to be conveyed is conveyed while the material is constrained by other conveyor rolls, a function of preventing, by the action of the speed control means, an excessive torque from being generated steadily is realized (for example, refer to Patent Literature 2).